Field of the Invention
The field of the invention relates generally to ophthalmic lens products and more specifically to lenses and lens blanks for eyewear, in which the lenses have a composite structure consisting of at least two disparate materials integrally bonded to each other.
Description of the Related Art
Ophthalmic lenses are commonly used to correct vision errors, aberrations and focusing deficiencies caused by age, disease or other factors. In addition to correcting physiological vision problems, ophthalmic lenses and eyewear may also be used to ameliorate physical or environmental conditions (such as glare, variable lighting, high intensity light, dust, condensation, etc.) that can affect sight. Eyewear may also incorporate aesthetic features for fashion and style.
In addition, ophthalmic lenses and eyewear must meet certain physical and performance requirements, such as impact resistance, temperature and chemical stability, structural integrity, durability, etc. For eyeglass lenses, it is important that the lenses and any coatings or features added to the lenses do not crack, chip, delaminate, discolor, haze or become detached from the lenses throughout the lifetime of use. These issues are particularly important to test and optimize when lenses comprise different materials, such as photochromic coatings; anti-reflective, absorptive or blocking coatings; filters; embedded films, layers, wafers or structures (such as polarizers, electro-active or conductive materials, displays, cameras, sensors, and the like), or combinations of two or more dissimilar optical materials.
The possible benefits of combining two or more optical materials to create a composite ophthalmic lens have been recognized for years. This has given rise to much work on coatings, embedded layers, inserts, and other layered materials. For example, U.S. Pat. Nos. 3,248,460 and 5,512,371 describes similar or different optical materials being added as discrete layers or structures to a base lens or preform, with the goal to provide other optical properties, such as a multifocal feature. U.S. Pat. Nos. 5,405,557 and 5,523,030 describe methods of making layered optical articles from at least two materials, one of which includes photochromic agents, but both of which are sufficiently similar in chemical composition that they create a homogenously layered article with no distinct phase boundary. In addition, polymeric optical materials have been proposed or are currently in use and comprise mixtures of various polymer systems, or comprise polymer(s) with added particles, fillers, capsules or other small structures of different chemical structure than the main polymer(s).
A significant and continued challenge is how to keep disparate materials sufficiently joined, without compromising their intended optical or other beneficial properties, throughout the lifetime of the ophthalmic lens. This is not a trivial challenge. The materials that are desirable to combine for optical or structural enhancement may have vastly different thermal, chemical, or mechanical response. For example, thermoplastics and thermoset materials by definition have distinctly different temperature responses and thermal structural integrities. In addition, some optical materials are much less affected by ultraviolet exposure than others, which can cause extreme and unacceptable damage in the form of embrittlement, yellowing or performance degradation (e.g., photochromic fatigue). Maintaining good optical performance of a composite ophthalmic lens can become even more difficult when common functional coatings (such as inorganic anti-reflective multilayer thin film coatings) are added to the lens. The composite structure alone, and in combination with common coatings, must remain well bonded and not suffer unacceptable damage, delamination, cracking, crazing or other defects when the lens is surfaced, polished, edged, drilled, tensioned or flex-fit into a spectacle frame. Additional or cumulative damage may occur from continued frame stress, or from other mechanical or environmental forces that act on the lens during everyday use. Any interface between dissimilar materials can easily become a weak point for initiation or propagation of damage or delamination.
Various techniques have been proposed to increase adhesion between dissimilar materials. For example, U.S. Pat. Nos. 6,256,152 B1, 6,531,076 B2, 6,585,373 B1 and 6,759,090 B2 describe various surface treatments that may be useful to improve adhesion between dissimilar layers or materials in composite optical parts. U.S. Pat. Nos. 6,413,641 B1 and 7,138,182 B2 further describe particular changes in the types or concentrations of chemical species or reactive groups that are present on polarizing films (or on inert polyethylene terephthalate films) and that may lead to improved adhesion with other optical materials. These varied prior attempts toward improved adhesion may point the way towards some candidate techniques, but also illustrate that neither a single nor an obvious choice of treatment, or of structural change, will universally result in beneficial adhesion. In fact, these patents indicate that notably different techniques and/or various compositional, structural or mechanical changes may be required to effect better performance. This will be dependent on the materials involved as well as the robustness of adhesion desired. For instance, if it is anticipated that the lenses may be exposed to extremes of temperature (such as Arctic conditions), different mechanical and temperature stabilities may be required as compared to “office lenses,” which are eyeglasses with the prescription optimized for a limited intermediate distance-viewing range suitable for computer work in an office setting. In addition, adhesion levels that may have been acceptable in previous eyeglass configurations may no longer be sufficient given current and evolving technologies. There are now more methods to process lens blanks into lenses, and more methods to secure lenses in eyeglass frames, given the advent of digital surfacing, 3D printing, rimless frames and other technology advancements. In addition, other components, such as displays, cameras, sensors, wireless electronics, connectors and displays that contain very dissimilar materials from typical eyeglass lenses and exhibit markedly different mechanical, physical and chemical behaviors from lenses, are increasingly being incorporated into ophthalmic lenses and are expected to perform reliably despite these new environments and multiple demands.
Thus, it is important to achieve and verify adhesion and lens integrity so that it is possible to create composite lenses of dissimilar materials with sufficient bonding to endure ophthalmic lens processing and provide good assurance of long-term performance for the patient.